Material handling vehicles and particularly automatic guided material handling vehicles have been utilized for decades to transport loads between spaced apart locations within storage, manufacturing and assembly facilities without the need for a vehicle operator. These vehicles were typically equipped with guidance systems which followed paths defined by stripes, wires, and other types of markers located on the floor. In order for the vehicle to be able to successfully follow the marked path, the floor must be smooth and free from imperfections such as, bumps, pot holes, and other obstructions. The need for the high quality floor and fixed guide path restricted the automatic guided vehicle usage to relatively simple transportation applications in new or remodeled facilities.
Advancements made in the area of computer technology during the last decade has provided for revolutionary changes in automatic guided vehicle technology in both the areas of vehicle guidance and load manipulation. An example of a guidance system for a new generation of automatic guided vehicles is shown in U.S. Pat. No. 4,647,784 to Philip E. Stephens dated Mar. 3, 1987 wherein a laser scanner mounted on the vehicle reads bar coded targets located within the facility and delivers this information to a computer located on the vehicle. The on-board computer calculates the location of the vehicle using triangulation, compares this information to a dead reckoning position of the vehicle and makes vehicle steering corrections when necessary. Dead reckoning of the vehicle is achieved by computer monitoring of vehicle sensors which sense wheel rotation, steering angle position and the like. As a result of this advancement in navigation the need for floor markings and smooth floors has been eliminated and the ability to travel to locations external of the facility for acquiring and depositing loads has been made possible.
In most material handling applications loads are placed on and removed from load carrying transporters such as, trailers, vans and the like docked at a receiving dock of the facility by manually driven fork lift trucks and the like. To load or unload a docked transporter by an automatic guided vehicle has been impossible in the past. However, with the birth of the free-ranging automatic guided vehicle discussed above the ability to load and unload a transporter is achievable.
In order to load and unload a load carrying transporter with an automatic guided vehicle the position of the docked transporter must be within an acceptable tolerance range from a nominal docking location so that the load may be moved relative to the load carrying transporter without damage to the load, the automatic guided vehicle and associated lift mast assembly, and load carrying transporter. Damage may occur when forceable contact between the load and side(s) of the docked transporter take place.
In situations where the automatic guided vehicle has deviated from a preprogrammed guide path or has become skewed relative to the load carrying vehicle, contact between the load and the sides of the load carrying transporter may take place which may cause damage as discussed above. The force caused by contact in either of the aforementioned situation may cause the vehicle to slide which will change the actual position of the vehicle and affect subsequent accuracy of vehicle navigation.
The lift mast assembly which carries the load is often at an angle relative to the vertical during the loading, traveling, and depositing process. The forces of gravity as well as vehicle dynamics acting on the load tend to move the load relative to the lift mast assembly. This affects the known position of the load and ultimately the deposit location. In situations wherein the attitude of the lift mast is forwardly inclined there is the potential for the load to inadvertently slide off the load engaging device carried on the lift mast assembly.
The present invention is directed to overcoming one or more of the problems as set forth above.